At present, in the field of wireless networks, the wireless local area network (WLAN) develops rapidly, and the application range of WLAN is increasingly expanding. To cope with various network requirements, the industry specification IEEE 802.11 task force of the Institute for Electrical and Electronic Engineers promulgated a series of most general WLAN technical standards such as 802.11ah, 802.11b, 802.11g and 802.11n, and then successively set up other task forces which work toward developing specifications relating to the improvements of the existing 802.11 technology. For example, with the development of the Internet of Things, IEEE set up the 802.11ah task force of which the main task is to modify and enhance the Medium Access Control layer (MAC layer) and the physical layer (PHY layer) of WLAN in order to accommodate the requirements of networks such as the Smart Grid, the sensor network, the Environmental/Agricultural Monitoring and the Industrial Process Automation.
In a wireless local area network, one access point (AP) and multiple non-AP stations (STA) associated with this AP constitute one basic service set (BSS). Before using a service of the BSS, an STA should complete the authentication and association process with the AP. If the STA successfully associates with the AP, the AP distributes, for the STA, association identification information which is called an association identifier (AID), wherein the AID is identity identification of the STA in the present BSS, that is, the STA can be distinguished from other STAs in the present BSS via their respective AIDs, however, STAs belonging to different BSSs may use the same AID. After being connected via a distribution system (DS) simultaneously, a plurality of BSSs may constitute one ESS (extended service set). A plurality of STAs may also constitute one self-organising wireless local area network which is called an IBSS (independent BSS), wherein in the IBSS, STAs are able to perform communications directly.
When a plurality of wireless stations share a channel, conflict detection in a wireless environment becomes very difficult, and one big problem is hidden stations. For example, station A sends data to station B, and at the same time, station C also sends data to station B, since station C is located outside the coverage range of station A and stations A is located outside the coverage range of station C, A and C sending simultaneously will cause conflicts. From the viewpoint of A, C is one hidden station. To solve the problem of hidden stations, 802.11 proposes a virtual channel detection mechanism, that is, by containing channel reservation duration information in the frame header of a wireless frame, other audit stations which receive the wireless frame containing the reservation duration information set one locally stored network allocation vector (NAV), wherein the value of the NAV is configured to be the maximum value of the above-mentioned reservation duration information, during which time, the audit stations will not send data, thus avoiding hidden stations competing for a channel and causing collisions. After the NAV reduces to zero, other stations can send data. For example, a sender sends an RTS (Request to Send) frame which contains channel reservation duration information to perform channel reservation, and a receiver replies with a CTS (Clear to Send) frame which also contains channel reservation duration information to perform channel reservation acknowledgement, so as to protect wireless frames subsequently sent by the sender. It should be noted that the frame for channel reservation which is sent for the first time, for example, the above-mentioned RTS, is not under protection, that is, the channel reservation duration value carried in this frame is used for protecting subsequent frame transmission, and the initial sending frames such as the RTS still have the risk of the collisions of hidden terminals. However, since the RTS frame per se is relatively short, the probability of collision thereof is small relative to longer data frames.
In addition, the trend of development of the traditional wireless local area network is to improve the transmission rate, satisfy users' requirements for high-throughput data services, and provide the QoS of the MAC layer. Furthermore, the wireless local area network has an acknowledgement mechanism of the MAC layer, which has the characteristics of transmission sequence control and automatic retransmission.
FIG. 1 is a schematic diagram of a frame with a traditional MAC frame header according to the related art. As shown in FIG. 1, there should be a frame control field in the frame header. FIG. 2 is a schematic diagram of the frame control field according to the related art. To satisfy the above-mentioned channel duration reservation mechanism, a traditional MAC frame header should carry a Duration/ID domain. To accommodate communications under the above-mentioned multiple network structures, for example, in an ESS, if STAs belonging to different BSSs need to communicate, they have to communication through associated APs and DSs of the two parties, and thus four MAC addresses, i.e. a transmission address (TA), a source address (SA), a receiving address (RA) and a destination address (DA) are necessary, and the MAC frame header of a data frame in a wireless local area network contains at least three MAC frame headers at present. To satisfy high throughput as well as QoS control and sequence control, there is also a corresponding control field in the frame header.
In networks such as a sensor network and a smart grid network, the services thereof generally have the following characteristics: there are a large number of STAs, but the traffic between the AP and each STA is small; a report service is generally completed in such a way that the STA sends a short data packet to the AP periodically or abruptly, and the time between two data transmissions is long; there is no service transmission between the STAs, that is, the MAC layer destination address of data reported by the STA is exactly the AP, and thus the network structure is simple and not too many MAC addresses are required. A typical example is that a smart meter sends information about the amount of electricity to an AP every several hours or even several days, and after receiving a response frame replied by the AP, the smart meter may not send data any more for a very long time. Since a data frame per se is very small in size, using a protection frame (RTS/CTS) to reserve a channel instead will increase the overhead. If the transmission does not require multiple frame exchanges, the reservation duration in the data frame is set to be one interframe space (IFS) and the transmission time of one response frame; and since there is no immediately subsequent transmission, no more duration needs to be reserved. This response to the data frame is immediate response, since it is unnecessary to transmit multiple frames successively, and functions such as link self-adaptation needs not to be used. Since the service of this network is relatively simple, even the sequence control and QoS control are unnecessary.
In a new application scenario of the wireless local area network, in a network such as a sensor network, the length of a data packet is generally 100-200 bytes. According to the existing protocols of the wireless local area network, during the transmission of short frames, the ratio of the overhead such as a physical layer frame header, a MAC frame header and a MAC acknowledgement mechanism to the data part is very large; therefore, it is proposed as one research subject in relevant WLAN task forces to reduce the overhead of the protocol, and there is no ideal solution in the related technologies temporarily.